chore(build): cache apt packages between runs

For now only in the windows docker. This saves a lot of bandwidth when
doing test builds locally.

windows/cross-compile/build.sh

@@ -97,10 +97,31 @@ fi
 
 readonly BUILD_DIR="/build"
 readonly DEP_DIR="$WORKSPACE_DIR/$ARCH/dep-cache"
+readonly APT_CACHE_DIR="$WORKSPACE_DIR/$ARCH/apt_cache"
 
+# Create the expected directory structure
+
+# Just make sure those exist
+mkdir -p "$WORKSPACE_DIR"
+mkdir -p "$DEP_DIR"
+mkdir -p "$APT_CACHE_DIR"
+
+# Build dir should be empty
+rm -rf "$BUILD_DIR"
+mkdir -p "$BUILD_DIR"
+cd "$BUILD_DIR"
 
 set -x
 
+echo "Restoring package cache"
+# ensure at least one file exists
+touch "$APT_CACHE_DIR"/dummy
+# restore apt cache
+cp -r "$APT_CACHE_DIR"/* /var/cache/
+
+# remove docker specific config file, this file prevents usage of the package cache
+rm /etc/apt/apt.conf.d/docker-clean
+
 
 # Get packages
 
@@ -145,18 +166,6 @@ fi
 set -u
 
 
-# Create the expected directory structure
-
-# Just make sure those exist
-mkdir -p "$WORKSPACE_DIR"
-mkdir -p "$DEP_DIR"
-
-# Build dir should be empty
-rm -rf "$BUILD_DIR"
-mkdir -p "$BUILD_DIR"
-cd "$BUILD_DIR"
-
-
 # Use all cores for building
 
 MAKEFLAGS=j$(nproc)
@@ -206,6 +215,14 @@ strip_all()
   set -e
 }
 
+# Store apt cache
+store_apt_cache()
+{
+  # prevent old packages from polluting the cache
+  apt-get autoclean
+  cp -r /var/cache/apt/ "$APT_CACHE_DIR"
+}
+
 
 # OpenSSL
 
@@ -360,6 +377,7 @@ if [[ "$TRAVIS_CI_STAGE" == "stage1" ]]
 then
   # Strip to reduce cache size
   strip_all
+  store_apt_cache
   # Chmod since everything is root:root
   chmod 777 -R "$WORKSPACE_DIR"
   exit 0
@@ -1070,6 +1088,7 @@ if [[ "$TRAVIS_CI_STAGE" == "stage2" ]]
 then
   # Strip to reduce cache size
   strip_all
+  store_apt_cache
   # Chmod since everything is root:root
   chmod 777 -R "$WORKSPACE_DIR"
   exit 0
@@ -1236,5 +1255,8 @@ fi
 cd ..
 rm -rf ./qtox
 
+# Cache APT packages for future runs
+store_apt_cache
+
 # Chmod since everything is root:root
 chmod 777 -R "$WORKSPACE_DIR"